Mmm. Sounds like an infection. You might need antibiotics. Did something get in her eye I wonder?
The crop is a part of the body which holds the grain or food after they swallow it, before it goes down into the gizzard to be digested. It feels like a little sac on the side of their neck. Sometimes there can be problems with the crop, like blockage or infection and that can affect their health and breathing. For example, I just had a hen die from "sour crop". Her crop felt all squishy and had a lot of fluid which would come up and choke her, so that' s why I was asking about it. But with your situation it sounds like something totally different.
Here is a link to other people who were dealing with eye problems and the advice they got. Read down to what they eye doctor had to say. https://www.backyardchickens.com/forum/viewtopic.php?id=36823
I agree tylan is the best option. You can use the water soluable type or injectable. 1cc for grown bird 1/2 cc for half grown or bantam. You can shoot the injectable type down the throat or inject into muscle for three days. Any bird that has been in contact will need to be treated as well.